In the field of energy production, there is a need for coal feeders. Currently, coal is fed to furnaces by screw feeders, but such devices are cumbersome, expensive, complicated, dirty or otherwise inefficient, or troublesome because they have required bearings and seals for fully rotating parts or an oil or sludge carrier. It is additionally advantageous to provide an accurately controlled feed rate, particularly when it is desired to feed coal to a high pressure, high temperature, reactor tube for producing fuel and other useful reaction products.